A significant number of products such as perishable foods, heat sensitive pharmaceuticals, electronics, and volatile chemicals require temperature monitoring during shipment to ensure the product has not been exposed to temperatures beyond a specific threshold that might engender degradation or malfunction of the product. Prior art temperature monitoring devices currently in use include: temperature labels containing visual indicator sections that change color, complex electronic data loggers, thermocouples, and probe thermometers. Among these, even the most cost effective solution (usually less than one dollar per unit) is still too costly for many manufacturers. Two of the most popular types of temperature monitoring solutions include: a liquid crystal (life temperature data) and sealed temperature sensitive chemical indicators which changes color permanently and irreversibly when exposed to elevated temperatures. Unfortunately, these irreversible sensors can only respond to narrow and specific temperature ranges which are usually limited to temperature difference of no more than about 50° Centigrade (C.). Therefore, the common solution for sensing a wide temperature range is accomplished by applying multiple sensors to the product during the shipping cycle, which is even less cost effective. Devices like data loggers or thermocouples are sensitive to much smaller changes and broader ranges, but are an expensive solution that in many cases might exceed the cost of the package being shipped. Therefore, there is a need for a low cost, thin temperature sensor that will register exposure to wide range of temperatures.
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